Starting control for electric discharge devices



March 20, 1945. TOWNSEND 2,372,149

STARTING CONTROL'FOR ELECTRIC DISCHARGE DEVICES Filed Feb. 12, 1942 z 36(Gr7ass) Invewtor: Mark A. Townsend, b5

His A'Hvorneg.

Patented Mar. 20, 1945 7 s'rm'rmo common FOR ELECTRIC mscnsaoa nnvrons Mark A. Townsend, Cleveland Heights, Ohio, asaignor to General Electric Company, a corporation of New York Application February 12, 1942, Serial No. 430,611

8 Claims. (Cl. 200-122) This invention relates to the control of electric discharge devices, and is especially concerned with the starting of such devices. The invention is very useful in connection with fluorescent tubes or lamps of the positive column discharge type, and is hereinafter explained with particular reierence to lamps of this character and their usual starting arrangements, as exemplified in U. S. Patent 1,951,112, March 13, 1934, to Wels, or Patent 2,212,427, August 20, 1940, to Peters, for instance.

Ordinary tubular fluorescent lamps have electrical starting circuits which are energized and mostats. With one of them may be associated an electric heater connected in the discharge circuit oi the lamp, while theother may atl'ord temperature compensation to prevent starting troubles in very hot or very cold weather. Such switches, however, are not readily adaptable to the wide range. of voltage and current under which they are required to operate, andpresent other drawbacks.

Through deterioration in service or as the result of accident, fluorescent lamps and other discharge devices often or eventually become incapable of starting and normal nmning, so that the only eflfect oi the automatic efforts to start such a lamp is a continual flashing in it that is very annoying to those in the area that receives the light of the flashing lamp, besides uselessly wearing out the starter device. Usually such incapacity for starting is due to loss of electron emission from one or both electrodes of the lamp, which may result from dissipation or other loss of activating material on which the emission depends. The objectionable flashing of such a lamp goes on indefinitely until the power supply is shut oil, or the lamp is removed from the circuit.

One aim of this invention is to obviate difliculties in the operation of starters due to the wide range of voltage and current under which they must operate. For this purpose, more or less separate means are provided ior closing and for opening the starting circuit, which can be more or less independently calibrated or adjusted according to the diverse conditions under which the circuit should be made and broken. Another purpose of the invention is to obviate the undesirable flashing of defective lamps without interfering with repetition of the attempts to start as long as there is any reasonable promise of success. This is accomplished by rendering the starter ineffective to close the starting circuit or ineffective to open it after repeated operation of the starter has failed to start the discharge. I have chosen this latter method for purposes of illustrative description, and I have shown and explained such a "lock-in feature in connection with a double thermal switch starter involving the feature oi separate control of the closing and opening actions, as above mentioned. However, it is to be understood that one of these features of the invention can be employed without the other, when desired. v I

Various other features and advantages of the invention will become apparent from the description of one species and form of embodiment, and from the drawing.

In the drawing, Fig. 1 is a diagrammatic view of a fluorescent tube or lamp with circuit connections including the present invention, a midportion of the lamp envelope being broken out and omitted; and Fig. 2 is a tilted or perspective view of one form of starting switch device.

Fig. 1 shows an ordinary fluorescent tube lamp L of the positive column electric discharge type with a tubular envelope in having spaced apart activated thermionic cathodes II, II in its ends, which may be specially heated cathodes oi usual coiled filament type, and are shown connected across a power-supply circuit P including the usual ballast M, which also serves as a starting inductance, and the manual make-and-break switch It. The envelope in may contain a lowpressure atmosphere of starting gas, such as argon at a pressure of 2 to 5 mm. of mercury, and also a vaporizable and ionizabie working substance such as mercury. A supply of mercury, which may exceed the amount that will vaporize during operation of the lamp L, is indicated by a drop i1 inside the envelope II, and an internal coating 01' fluorescent material or phosphor II on the envelope walls is also indicated. A starting and electrode-heating circuit H is shown connected across the circuit P through thev filamentary cathodes l I, II, with a starting switch 8 included therein, which may be of thermal type. A capacitor or condenser IQ of suitable capacity (e. g., 0.007 microiarad) may be connected across contact members.

the switch s. to minimize radio interference as well as arcing when the switch S opens and breaks the-circuit H.

' The general mode of operation in starting the lamp L with this circuit arrangement is that when the switch 15 is closed to turn on the lamp L, the switch device S permits flow of current through the circuit H and the cathode filaments ll, ii in series therein for a sufflcient length of time to preheat the cathodes toan adequate emissive temperature, and then suddenly opens the circuit H; and the resulting voltage kick between the cathodes H, H sufiices to initiate discharge between them'-or, in other words. starts the lamp.

As shown in Figs. 1 and 2, the switch device 5 is a thermal switch comprising switch members 2 I, 22 that are connected to opposite sides of the starting circuit H and coact in making and breaking this circuit. For convenience, these switch members 2|, 22 may be distinguished'as first and "second switch members, respectively. The switch members 2|, 22 may consist of slender, straight, approximately upright thermo 22. In the present instance, this contact}! and its connection consist of an extension or the leadwire 3| upward and to the right, Fig. 2, and down into the path of the heat-responsive circuitopening thermostat switch member 22.

The heater 25, which is subject-and responsive to the high ballast output voltage when the switch S opens, is preferably of very high resistance, such as 100,000 ohms, for example, in order to prevent it from seriously lowering the voltage available for starting the discharge. It may also be found advantageous to make the heating resistance 25 or a type having a negative temperature-resistance coemcient, so that it may heat more rapidly and cause the member 2| to close the switch more quickly, yet not move far enough to close under the normal operating volt age of the lamp. The heater 28, through which right in Fig. 2. Adjacent the thermostat members 2|, 22, about concentric with their bends 26,

24, there are resistance heaters25, 26 for heating these members. The circuit connections of these heaters will be more fully described hereinafter; for the present it suffices to say that the heater 25 for the member 2| is connected across the circuits H and P in parallel with the members 2|,

22, so as to respond essentially to the energization and voltage of the main discharge circuit P during startin (1. 8., said heater 25 provides a current conducting path shunting the contacts 23, 23) while the heater 26-for the member 22 is connected in the circuit H in series with the members 2|, 22 so as to respond to'the energize ation of this starting circuit H and to the current flow therein. The thermostatic switch members 2|, 22 may be arranged-to flex in the same direction (towardthe right in Fig. 2) when heated, and vice versa. 2 v 1 =The switch S may comprise as its base a hollow glass stem 30 into which. are sealed or fused four wires 3|, 32, 33,35. The wires 3|; 32 which serve as the switch leads are connected to opposite sides of the starting circuit H, and the lead wire 3| carries the switch member 2 w ch 2 has its lower end welded to this wire. The 0 her lead wire 32 is bent to extend nearly horizontally, and serves as a common connection for corresponding ends of the resistance heaters 25, 26. The wire 33 which forms the other end connection or the heater 25 is connected to the wire 3|,

and the wire 34 which forms the other end conflows the cathode preheating current in the starting circuit H when the switch S is closed, is preferably of low resistance, such as 3'ohms, in order to minimize its energy consumption. Any suit= able provision may be made to cause the heater 26 to heat the thermostat 22 and to cool ofl rather slowly, such as enclosing this heater 23 in a glass sleeve .36, so as to give it a high heat capacity. 0n the other hand, the heating and cooling time of the heater is may be minimized, as by blackening it so as to lower its heat capacity.

When the switch it is closed for a cold start. line voltage is applied to energize the circuits P, H and the heater 2e, and the thermostat member 2i is heated and flexes to the right into contact at 23 with the member 22, closing the switch 8 and fully energizing the circuit H and the heater 25. Closing of the switch 8 short-circuits heater 25, which is thus tie-energized and starts to cool on, as well as thermostat 2|. The current flow through the cathode coils ii, ii and the heater 2t preheats the cathodes and also heats up the thermostat member 22, which flexes to the right out of contact with the member 2|, breaking the circuit H. This opening of the starting circuit heater 26 and the thermostat 22 are de-enersized, and the de-energlzed thermostat 22 cools and unfiexes to the left. The discharge in the lamp L shunts or short-circuits and tie-energizes the heater 25 (in view oi its high resistance) suf- Iiciently to prevent it from reclosing the switch 8. If this cycle of operation or the switch 8 fails to start the lamp L,'it maybe repeated oneor more times. In the case of a defective lamp, repeated cycles of operation or efforts of the starter S to start the discharge result in a gradual accumulation of heat in the heaters 25, 26 and in the thermo- 'stats 2|, 22, so that the ranges of movement of these members'2|,'22 in the successive efforts to start gradually shift over more and more to the right, toward the contact 35. Accordingly. ach

futile efiort to start takes p ace with the members 2|, 22 further over toward the contact 35. When the member 22 (or the projecting upper end of its contact 23) touches the contact 35,

the switch S and the heater 25 are both shortcircuited or shunted out, so that this heater and heat-responsive movement of one of the members 2|, 22, and is connected to the same, sideof the circuit H as the other of the members 2|,

the member 2| cool on, the member 2| unfiexes to the left, and the starting efforts of switch .8 are suspended; "but current continues to flow through the starting circuit H and the heater 2', thus keeping the member 22 against the contact l and maintaining the closed condition 01' the circuit H, so that the lamp cathodes II, I l are heated continuously and steadily. Thus the switch S "locks in."

However, if the circuit H is de-energized (by 1 opening the hand switch II, or by removing the cent lamps of the usual positive column type are given: a

The thermostatic members 2|, 22 ma be strips of the bimetal commercially knowntas Chace #2400 Bimetal, composed of laminae of Invar,

an alloy oi 64 per cent iron and 36 per cent nickel, and of chrome iron, an alloy of 75 per cent iron, 22 per cent nickel, and 3 per cent chromium, in equal thicknesses, welded together. Each of the strips 2i, 22 may be 0.004 inch thick, and V8 inch wide, and 19 mm. long before being bent. The lengths of their lower straight portions to which the wires 3|, 24 are welded may be 0.195 inch, and the diameters of their bends 24, 24 may be 0.110 inch. The horizontal distance apart of the portions to which the leads 3|, 34 are attached may be /4 inch. The contacts 23, 23 may be of 40 mil coin silver wire. The gap between the contacts 23, 23 when the switch is cold may be 0.04 inch, and that between the parts 22 and 35 may be about 0.1 inch. The heater 2! may be a helical coil or about 42 mm. of "Nichrome" wire at 0.0063 inch diameter wound on a 40 mil mandrel, and its surrounding sleeve 25 may consist of a 5 mm. length of gage nonex glass tubing. The heater may be a solid rod of high resistance material of 1; inch diameter inch long, showing a resistance of 100,000 ohms under a voltage of 100 volts D. C., and characterized by a negative temperature-resistance coefiicient-such as the material commercially known as "Globar BNR. The "Nichrome above referred to is an alloy consisting of 75 per cent nickel, 12 per cent iron, 11 per cent chromium, and 2 per cent manganese.

What I claim as new and desire to secure by Letters Patent 0! the United States is:

1. A thermal switch comprising normally spaced cooperating first and second contacts, means providing a current conducting path shunting said contactsmeans responsive to heat produced by current in said path for moving said first contact into engagement with said second contact, heating means arranged to beconnected into circuit by engagement of said contacts, means responsive to heat produced by said heating means for moving said second contact away from said first contact whereby said contacts alternately engage and disengage each other, and a third contact located in the path 01' movement of said second contact and electrically connected to said first contact so that heat accumulated by the heat responsive means of said second contact during a plurality of successive intervals of current flow in said heating means causes said second contact to engage said third contact and thereby terminate i'urther iunctioning oi the contact moving means.-

2. A thermal switch comprising normally spaced cooperating first and second contacts, a high resistance heater shunting said contacts, means responsive to heat produced by current in said heater for moving said first contact into engagement with said second contact, a low resistance heater connected to said second contact in series with the gap between said contacts, means responsive to heat produced by said low resistance heater for moving said second contact away from said first contact whereby said contacts alternately engage and disengage each other, and a third contact located in the path of movement of said second contact and electrically'connected to said first contact so that heat accumulated by the heat responsive means of said second contact during a plurality of successive intervals of current flow in said low resistance heater causes said second contact to engage said third contact and thereb terminate further functioning of the contact moving means,

3. A thermal switch comprising a support, first and second bimetallic strips secured thereto at one end and having normally spaced co-operating contacts carried by their free ends, said strips being arranged to move their contacts in the same direction when heated, a first resistance heater connected between said strips and arranged to heat said first bimetallic strip to car y its contact into engagement with the contact on said second strip, a second resistance heater connected to said second strip in series with the gap between said contacts so that current flows therethrough upon engagement of said contacts, said second resistance heater being arranged to heat said second bimetallic strip to carry its contact away from the contact on said first strip whereby said contacts alternately engage and disengage'each other, and a stationary contact located in the path oi movement 01' said second strip and electrically connected to said first strip so that heat accumulated by said second strip during a plurality of successive intervals of current flow in said second resistance heater causes said second strip to engage said stationary contact and thereby terminate further functioning of said strips.

4. A thermal switch comprising normally spaced cooperating first and second contacts arranged ior movement in the samedirection,

means providing a current conducting path shunting said contacts, means responsive to heat produced by current in said path for moving said first contact into engagement with said second contact, a resistance heater connected to said second contact in series with the gap between said contacts, and means responsive to heat produeed by said resistance heater when the contacts are closed for moving said second contact away from said first contact.

switch member when the switch has been closed, and thus opening the switch.

6. A thermal switch comprising normallyj spaced cooperating first and second contacts arranged for movement in the same direction,

means providing a current conducting path away from said first contact whereby said con tacts alternately engage and disengage each other, and means arranged to engage the moving means for said second contact and terminate further functioning thereof upon accumulation oi heat therein during a plurality of successive in= tervals of current flow in said resistance heater.

'7. An, automatic starter for connection in a starting circuit of a discharge device, for interrupting said starting circuit to start the discharge in said discharge device, said starter comprising coacting switch members for connection respecv asvaue tiveiy to opposite sides of said circuit, and a shunting contact connected to one of the aforementioned switch members and located in the path of the circuit-opening movement of the other of said aforementioned switch members, for engaging the last-mentioned switch member and thus closing the circuit regardless of contact or separation of said aforementioned switch members.

8. A thermal switch comprising coacting first and second switch members for connection to opposite sides of a circuit, with an actuating thermostat for moving the second switch memher in a direction away from the first switch member to open said circuitwhen said thermostat is heated, a heater for said thermostat that is traversed and heated by current flowin through said thermal switch when closed, and a shuntins contact connected to the first switch member and located in the path of the heatresponsive circuit-opening movement of the second switch member, for engaging said second switch member and thus closing said circuit resardiess of contact or separation of said first and second switch members.

MARK A. TOWNSEND. 

